1. Field of the Invention
The present invention relates to a bandwidth monitoring method for monitoring a bandwidth for each packet which flows into a network, and a bandwidth monitoring device therefor.
2. Description of the Related Art
Traffics (packets), which flow over an Internet, are increasing rapidly with an increase in Internet users. In a packet type communication system employed in the Internet, packets sent from a large number of users can be transmitted through the use of the same line. It is therefore possible to reduce the cost per bandwidth. With a view toward achieving the low cost of the packet type communication system, moves have been made to integrate telecommunication networks and enterprise networks which have heretofore been achieved by private networks, into one by the Internet thereby to implement a reduction in communication cost. It is necessary to implement quality of service (QoS) such as low latency, low discard probability, etc. which have been achieved by the conventional telecommunication networks or enterprise networks for the purpose of integrating these into one.
As a prior art related to QoS, there is known, for example, a Diffsery (Differentiated Service) (hereinafter called prior art 1) described in RFC2475 of IETF (Internet Engineering Task Force). The prior art 1 describes that traffics (packets) are divided into classes by a source/destination IP address, a source/destination port number, a protocol, etc. in a TCP/IP header at an entrance of a network which provides services, and forwarding operations are assigned thereto. Further, the prior art 1 also describes that each packet is transferred based on a transfer or forwarding operation related to a DSCP (Differentiated Service Code Point) in a header in the network.
A node at the entrance of the network assigns preferentially packet-transferred forwarding operations to packets each of which needs low latency and low discard probability, and each node lying within the network forwards the packets preferentially, whereby the low latency and low discard probability of the packets can be achieved. Incidentally, packets to which preferentially packet-transferred forwarding operations are assigned, and packets other than the packets will be called priority packets and non priority packets respectively.
A network for implementing QoS makes a contract for a bandwidth of priority packets with a user. The node at the entrance of the network has the function of performing bandwidth monitoring and performs monitoring at the bandwidth (bandwidth monitoring or check). The bandwidth monitoring function has been described in, for example, the prior art 1.
The prior art 1 describes that a contract for forwarding-operation decision rules (for example, voice packets are transferred preferentially, etc.), a bandwidth, etc. (TCA: Traffic Conditioning Agreement) is established between the user and the network, and the node at the entrance of the network discards packets or changes DSCP so as to satisfy the TCA. Owing to the bearing of the bandwidth monitoring function by the node at the entrance of the network, a large amount of priority packets sent by one user can be prevented from flowing into the network, and QoS of priority packets sent from other users is achieved.
The bandwidth monitoring function is common as an ATM (Asynchronous Transfer Mode). Bandwidth monitoring executed in the ATM has been described in, for example, Chapter 4.5 of The ATM Forum Specification version 4.0 (hereinafter called prior art 2). In a VBR (Variable Bit Rate) service described in the prior art 2, a user makes a contract for a maximum bandwidth (PCR: Peak Cell Rate) and an average bandwidth (SCR: Sustainable Cell Rate) with a network. The user sends out each cell with CLP (Cell Loss Priority) indicative of priority of a cell discard in a cell header as priority (=0: hard to discard a cell) and non priority (=1: easy to generate a discard) according to the degree of importance. Further, the prior art 2 describes that packets having CLP=0 are monitored at an average cell rate, thereby to discard a violation packet (called VBR. 2) or to set the CLP of violation cells to “1” (called VBR. 3). By allowing a node at an entrance of a network to hold such a bandwidth monitoring function, QoS in an ATM network is achieved.
In the prior art 1, the user might not be able to sufficiently use the contract bandwidth when the DSCP is judged according to the forwarding-operation decision rules. A description will be made of a case in which a bandwidth for priority packets is contracted under the decision rules for determining the voice packets as the priority packets and the packets other than the voice packet as the non priority packets.
The bandwidth monitoring device having the bandwidth monitoring function according to the prior art 1 judges voice packets lying within a monitoring bandwidth as priority packets, and voice packets at the monitoring bandwidth or higher and packets other than the voice packets as non priority packets. When traffics sent out by a user are shown in FIG. 8(a), traffics subsequent to the passage of the bandwidth monitoring function are represented as shown in FIG. 8(b). Packets other than the voice packets indicated by diagonally-shaded portions shown in FIG. 8(b) are transmitted as non priority packets regardless of the fact that the priority packets fall within the monitoring bandwidth. Namely, the user is not able to sufficiently use the contract bandwidth for each priority packet.
On the other hand, even the prior art 2 will cause a problem similar to the above. The bandwidth monitoring device having the bandwidth monitoring function according to the prior art 2 transmits only cells with CLP=0 within the monitoring bandwidth as CLP=0. When traffics sent out by a user are given as shown in FIG. 15(a), traffics subsequent to the passage of the bandwidth monitoring function are represented as shown in FIG. 15(b). Cells corresponding to the diagonally-shaded portions in FIG. 15(b) are transmitted as cells with CLP=1 regardless of the fact that the amount of cells with CLP=0 is within the limit of the monitoring bandwidth. Namely, the user is not able to sufficiently utilize a contract bandwidth with CLP=0.